Pressure fluid servomotor



June 3, 1947.

T. H; THOMAS' PRESSURE FLUID SERVOMOTOR Filed Nov. 21, 1945 INVENTOR. 7i/M4JA/ 72 0/74;

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Patented June 3, 1947 UNITED STATE mns'sonn'rwm sanvomo'ron Thomas H. Thomas, South Bend, Ind. Application November 21, 1945, Serial No. 629,956

' This application has to do with pressure fluid Specifically. it IS an object of this invention to simplify the construction and operation of a. double-acting power cylinder by providing a reaction or feel producing member which operates inone direction only;

Other objects and advantages will become apparent during the course of the following description, reference being had to the accompanying drawings, in which:

Figure 1 is a vertical section taken through a power control device incorporating my invention; and

Figure 2 is a plan view of a portion of the power control device of Figure 1.

In the drawings I have shown a power device comprising a cylinder I2 adapted to be supported on the vehicle frame by means such as the connection i4, and a pressure responsive movable member or piston l6 reciprocable in the cylinder l2. It will be obvious from the description that a diaphragm type of power unit, i. e., a power unit in which piston I6 is replaced by a diaphragm pressure member, can be used equally well within the scope of the present invention. The piston l6 divides cylinder l2 into two chambers l8 and 20, the arrangement being such that movement of the piston IS in either direction is caused by' creation of a pressure differential over said piston. In other words, by introducing a relatively low pressure into chamber l3 and a relatively high pressure into chamber 20, the piston IE will be moved to the left, whereas, by introducing a relatively low pressure into chamber anda relatively high pressure. into chamber l8, piston l6 will be moved toward the right. This arrangement is generally referred to as a doubleacting power unit, in order to distinguish it 3 Claims. (01.121-41) from the type of power unit in which the power acts in one direction only and a spring returnsthe unit to released position.

Control of this power unit can conveniently b accomplished by a valve member 22 moving inside a tube 24. The valve member 22 is moved by the vehicle operator, and the tube 24 is secured to piston l6. Tube 24 is also connected to the mechanism which is to be operated, such as such as the vacuum provided by the conventional intake manifold. The vacuum source thus communicates through passage 30 with the annular chamber 32 formed between land 33 and land 35 of the valve member. A source of higher pres! sure, such as the atmosphere, communicates through tube 34, passage 38 and the interior of boot 38 with openings 40 in tube 24 which lead to an annular chamber 42 formed between the stem 26 of the valve member and the wall of tube 24, the ends of chamber 42 being defined by land 35 and flange 43 on stem 26. Through a passage 44, chamber 42 is in communication with an annular chamber 46 provided in the valve member between land 33 and land 41.

Mounted upon and movable with power piston I8 is a reaction member 48,- which may be constituted by a diaphragm 50 supported between a pairof plates 52. This reaction member is secured by suitable means, such as a nut 54, to valve member 22. The peripheral portion of the reaction member 48 may be supported on a cupshaped member 56 which is secured to the tube 24 and piston l6. At the opposite side of reaction member 48, a housing or cover member 58 provides, in combination with said reaction member, a chamber 60 which isclosed except for a passage G2leading therefrom to passage 44 and thence to the atmosphere. In the illustration the housing 58 has an outwardly extending flange 64 which serves as a retainer for the sealing means 66 of power piston l6. Chamber 68, formed at the side of reaction member 48 opposite chamber 60, is at all times in communication with chamber l8 through openings 10 provided in member 56 and openings 12 provided in the flange of housing 58.

Operation of my improved power device is as follows. The usual pedal or other manually conto the left, pushing hollow stem 26 to move valve member 22 toward the left. Prior to movement of valve member 22, ports 82 and 84 provided in tube 24 are cut off from communication with vacuum chamber 32 by means of the lands 33 and 35. Preferably, the distance between the left edge of port 82 and the right edge of port 9 3 84 is slightly greater than the distance between the left edge ofland 33 and the right edge of land 35, in order that, in released position. atmosphere chamber 42 will be connected to power cylinder chamber 20 and atmosphere chamber .48

will be connected to power cylinder chamber l8.

of the power cylinder communicates with the atmosphere.

A pressure differential is developed over power piston It, the air in chamber 28 acting against the vacuum in chamber l8 to move piston l6 toward the left; This movement of the piston exerts force through tube 24 to operate the brakes or other controlled mechanism.

As the pressure in chamber I8 is reduced by evacuation of the air-therein, a pressure differential is developed over reaction member 48, since air at atmospheric pressure is present in chamber 68, While chamber 88 is in communication with the vacuum source through port 82. This pressure acts against thepressure exerted by the operator, tending to move valve member 22 toward the right, and thereby creating a feel, which is .a resistance proportional to the power developed by piston l6. This feel or reaction" indicates to the operator the progressive increase in pressure being applied to the brakes. movement of piston l6 toward the left carries with it tube 24, the operator must continue tomove valve member 22 toward the left if he wishes to maintain communication between port 82 and chamber 32 and between chamber 42 and port 84. This is true because tube 24 follows up the valve member and will overtake it and bring the power device to lapped position if leftward movement of the valve member is discontinued. When lapped position is obtained, the power devlce'remains as it is, without further applying the brakes and without releasing the brakes, until the operator desires either further actuation or release.

When the pedal is allowed to return to released position, valve member 22 moves toward the right under the influence of the pedal return spring and the pressure differential acting over reaction member 48. This movement of valve member 22 brings atmosphere chamber 46 into registry with port 82 and brings vacuum chamber 32 into registry with port 84, thereby connecting the atmosphere to chamber l8 and connecting the vacuum source to chamber 28; This reversal of the pressure differential over piston I8 causes a rapid return movement of said piston toward the right. During this movement the pressure in chamber 68 gradually increases until it equals the pressure in chamber 80, thereby neutralizing the effect of reaction member 48.

Since chamber 60 is at all times in communication with the atmosphere, there can never be a pressure differential over reaction member 48 acting toward the left. It is important that the reaction diaphragm be operative during one direction of power piston movement only. If each side of the diaphragm were to be exposed to the pressure in the opposite end of the cylinder, it would be necessary to incorporate avalve return spring of sufficient load to overcome the. full reaction of the diaphragml Otherwise, the cylinder would not be held in the released position Since I a 4 under full power; and manufacturing tolerances and the like would cause some units to be held in theirreleased position with very little pressure diflerence across the piston, while other units would be held with considerable pressure difference across the piston. Incorporation of a heavy valve return spring makes it very dimcu'lt to obtain initial application of the brakes with a low force on the valve member.

It will be apparent that the invention may be utilized in a system wherein the high pressure source is something other than air at atmospheric pressure and/or the low pressure source is something other than intake manifold vacuum. However, the present embodiment would be preferred for ordinary commercial usage.

If, for any reason, the power device should fail to operate, the brakes may be manually applied vention has been described, it will be understood by those skilled in the art that the object of the invention may be attained by the use of construc- 1 tions different in certain respects from that disclosed" without departing from the underlying principles of the invention, I therefore desire by the following claims to include within the scope of my invention all such variations and modifications by which substantiall the results of my invention may be obtained through the use of substantially the same or equivalent means.

Iclaim:

1. Vacuum power means for creating brake applying pressure comprising a power cylinder, a piston dividing said cylinder into two chambers and arranged for movement therein under the influence of a controlled pressure differential, a diaphragm mounted in thecenter of said piston, a housing member carried by the piston covering one side of the diaphragm and forming with said diaphragm a chamber, a tubular member connecting said piston to the brake applying means to operate the same, and a valve slidable. in said tube to cooperate therewith in when moved in one direction relativeato the tube causing one of the chambers to be connected to vacuum and the other to be connected to atmosphere and when moved in the opposite direction relative to the tube causing the connections to be reversed, thereby obtaining a power stroke of the piston in both directions, said valve being secured to the diaphragm at one end and to an operator operated member at the other end, said valve being provided with a passage-permanently permitting communication between the atmosphere and the chamber formed between the diaphragm and the housing member, the other side of the diaphragm being acted upon by the pres sure prevailing in the chamber at the opposite side of the piston to thereby cause a force proportional to that actin on the piston to react through the valve upon the operator operated member in one direction only of movement of piston, means carried by the piston enclosing the diaphragm to form a chamber on each side thereof. a tubular member connecting saidpiston to the brake applying means to operate the same, and a valve slidable in said tube to cooperate therewith in controlling the connection of atmosphere or a vacuum source to the'chambers at opposite sides of the piston in the power cylinder,

said valve when moved in one direction relative to the tube causing one of the chambers to be connected to vacuum and the other to be connected to atmosphere and when moved in the opposite direction relative to the tube causing the connections to be reversed, thereby obtaining a power stroke of the piston in both directions, said valve being secured to the diaphragm at one end and to an operator operated member at the other end. said valve being provided with a passage permanently permitting communication between the atmosphere and the side or the diaphragm which is the forward side during the pressure stroke, the other side of the diaphragm being in communication with the power cylinder chamber which is forward during the pressure stroke to thereby cause a force prop rtional to that acting on the piston to react through the valve upon the operator operated member in one i direction only or movement of the piston.

3. In a power device having a casing and a pressure responsive movable member therein dividing said casing into two chambers, manually operable valve means movable in one direction to cause a pressure diflerential over said pressure responsive movable member tending to move it in a given direction and movable in the other direction to cause a pressure diflerential over said pressure responsive movable member tending to moms H. moms. 

